High quality video display is an important feature in desktop computer systems. In systems based on the Pentium processor sold by Intel Corporation, and which utilize the Windows operating system, the MPEG compression standard is typically used. The compressed video is encoded in YUV space, in which, in the YUV12 format, consists of a plane of Y data, i.e. a grey scaled portion or luminance of the video image, and two planes of data respectively called U and Y data, which is the color or chrominance portion of the video image. The U and V planes are subsampled by two. Thus, for a 352.times.240 pixel video image, there exists a 352.times.240 pixel Y plane and two 176.times.120 pixel U and V planes.
On the other hand, the graphics display of such computers exists in RGB space, which can be considered as three overlaid planes of red, green and blue intensities In a graphics system of the desktop computer which is to display video, the video signal must be converted from YUV space to RGB space.
The planes of data and their transformation are illustrated in FIG. 1. A 352.times.240 pixel Y plane of data 1 and corresponding 176.times.120 pixel U and V planes 2 each of 1/4 the size of the Y plane (having been subsampled in each direction by two), is converted to the three R, G and B planes 3 which define the RGB form of image to be displayed on the computer monitor.
Conversion is performed by a matrix multiplication EQU R=1.164(Y-16)+1.596(V-128) EQU G=1.164(Y-16)-0.813(V-128)-0.39(U-128) EQU B=1.164(Y-16)+2.018(U-128).
This is computationally expensive and is often accelerated in special purpose hardware with a digital signal processor (DSP) The Intel Pentium P5 processor does not support the level of DSP functions required to be able to convert a single pixel in a single cycle.
Typically, for optimal conversion when a computationally expensive process is required, a table lookup scheme is used. All the calculations for the complete set of possible parameters are pre-computed into a table, and the parameters are used as indeces to that table. This gives the minimum computation time, but can require an enormous amount of memory for the table. In this case, the YUV data values would be accepted as an index into a table of RGB data values.